Supercharger with heat insulated gear case

ABSTRACT

A positive displacement supercharger includes a housing having a rotor cavity. A pair of positive displacement rotors are oppositely rotatable in the rotor cavity and have interleaved helical lobes forming rotor chambers operative to carry air axially from an inlet end to an outlet end of the cavity. A gear case adjacent the rotor cavity is drivably connected with and supports the rotors, the gear case including a bearing housing having an end surface facing the rotor cavity and the outlet ends of the rotors. A heat insulating material is applied to the end surface of the bearing housing and is effective to reduce heat flow between the rotor cavity and the end surface of the bearing housing to effectively reduce lubricating oil temperatures in the gear case. The insulating material may be a ceramic plate fixed to the bearing housing end surface.

TECHNICAL FIELD

This invention relates to positive displacement compressors or superchargers, such as roots type or screw compressors utilized for automotive engine superchargers and other purposes.

BACKGROUND OF THE INVENTION

It is known in the art to utilize positive displacement compressors having lobed rotors for supercharging internal combustion engines and for providing compressed air for other purposes. Such a compressor used as an automotive supercharger may include a housing having a rotor cavity in which a pair of parallel rotors having interleaved lobes rotate to compress air drawn into one end of the housing and discharged through an opening in the cavity wall near an opposite end of the housing. The rotors may be belt driven by the engine through a pulley connected directly, or through a gear train, to the pair of rotors.

Roots type and screw type compressors used on original equipment automotive engines are made with a bearing housing between the rotors and the supercharger gear case. This bearing housing is made of aluminum on some commercial superchargers. The aluminum rotors have their compressed air outlet ends rotatably mounted adjacent the bearing housing and are supported and driven through rotor drive stubs extending into the gear case The bearing housing and gear case are sealed by a front cover to form a drive assembly provided with a permanent charge of oil for lubricating the gears and bearings. The gear case has no positive cooling other than ram air in an automotive installation.

Boost operation of the supercharger increases the air temperature at the outlet ends of the rotors next to the bearing plate with the highest temperatures reached at maximum engine speeds. The boosted air heats the gear case oil by forced convection/conduction through the aluminum bearing plate At high boost levels, this can lead to unacceptable gear case temperatures at continued high speeds and loads. This in turn may require speed limits or boost trim to prevent gear case oil damage or seal damage that can lead to catastrophic supercharger damage.

Dynamometer tests of a supercharger have shown that the gear case heats up very rapidly at high speeds without supplementary cooling of the gear case. This problem is limited in some vehicle installations because continuous maximum speed operation is not possible for most vehicle installations. However, with less under hood air flow and/or higher continuous speeds, the gear case temperatures could exceed design limits. Methods and means are desired for limiting supercharger gear case oil temperatures during severe operating conditions.

SUMMARY OF THE INVENTION

The present invention results from consideration of both practical and low cost means for limiting gear case oil temperatures of a positive displacement supercharger.

Since high temperature of the compressed air at the discharge end of the compressor rotor cavity appears to be a main source of heat flow to the gear case oil, the present invention is designed to reduce the rate of heat flow between the rotor cavity and the gear case oil of a supercharger.

The heat flow may be reduced by applying a suitable insulating material between the rotor cavity and the associated bearing housing of the supercharger.

In a selected embodiment, the insulating material is a ceramic suitable for high temperature applications.

In accordance with the invention, a heat resistant insulating ceramic material may be applied to a face of the aluminum bearing housing that faces toward the rotor cavity and the rotors operative therein. The ceramic material may be in the form of a preformed plate having substantial strength for operation adjacent the rotor cavity and the ends of the rotors. The plate may be secured to the bearing housing by any suitable means including, for example, adhesives or mechanical fasteners.

If desired, other forms of heat insulation may be applied in any suitable manner to the cavity facing face of the bearing housing. Alternatively, or in addition, other forms of insulation or insulators may be applied between the rotors and extensions thereof into the gear case to further reduce heat transmission to the gear case oil.

These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exterior pictorial view of an exemplary helical rotor supercharger according to the invention;

FIG. 2 is a partial cross-sectional plan view showing the insulated interior of a supercharger similar to that of FIG. 1.

FIG. 3 is an interior pictorial view of the supercharger of FIG. 2 with the bearing housing omitted to show the insulating plate; and

FIG. 4 is a face view of the insulating plate.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Referring first to FIG. 1 of the drawings in detail, numeral 10 generally indicates a positive displacement helical lobed compressor or supercharger according to the invention. Supercharger 10 includes a rotor housing 12 having an internal rotor cavity 14 defined by a surrounding wall 16 and front and rear end walls 18, 20 respectively. A generally rectangular inlet opening 22 in a lower portion of the rear end wall 20 communicates an inlet end 23 of the cavity 14 with a source of inlet air, not shown. A generally V-shaped outlet opening 24 extends through the surrounding wall 16 adjacent the front end wall 18 of the housing and communicates an outlet end 25 of the cavity 14 with a pressure charging air system, not shown.

Within the cavity 14 there are rotatably mounted a pair of supercharger rotors 26, 28 having lobes 30, 32 with opposite helix angles, as is best shown in FIG. 2. The lobes 30, 32 of the rotors are interleaved in assembly to define with the housing helical rotor chambers 34.

The rotors form a rotor assembly 36 having inlet and outlet ends 38, 40. The rotor assembly 36 is belt driven through a pulley, not shown, connected with a drive gear case 42 to form a drive and rotor assembly 44.

The gear case 42 includes a front cover 46 and a bearing housing 48 enclosing a timing gear train 50 and bearings 52, which drive and support the outlet end 40 of the rotor assembly 36. Bearing housing 48 includes an inner end surface 54 facing the rotor cavity 14 and the rotor assembly outlet end 40 The rotors are of the helical Roots type, although a screw type supercharger having air compressing screw type rotors could be used if desired. The rotor chambers 34 carry charging air from the inlet end 23 to the outlet end 25 of the rotor cavity 14.

In accordance with the invention, the inner end surface 54 of the bearing housing 48 is covered with a suitable insulating material, such as a temperature resistant ceramic, preferably in the form of a preformed ceramic plate 56, best shown in FIGS. 3 and 4. It is formed with an outer periphery 58 configured to cover the inner end surface 54 of the bearing housing (not shown in FIG. 3) with openings 60 for the rotor drive shafts, not numbered. The plate may be fixed to the end surface 54 of the bearing housing 48 by any suitable means, such as high temperature adhesives or mechanical fasteners. Alternatively, other forms of insulation could be applied in place of or in addition to the described ceramic plate.

In operation, the supercharger 10 draws air into the inlet end 23 of the rotor cavity 14 and carries it to the outlet end 25 of the rotor cavity where it is discharged at a higher pressure and temperature. As the rotor speed is increased to a maximum, the air outlet temperature is raised to a limit, which, if conducted into the gear case 42 through the aluminum material of the bearing housing 48, could overheat the lubricating oil in the gear case and possibly damage the oil and oil seals, not shown. However, the addition of the ceramic plate 56, or other insulation, on the inner end surface 54 of the bearing housing 48 substantially reduces the conduction of heat into the gear case 42 and reduces the operating temperature of the oil in the gear case. This protects the gear case against excessive oil temperatures and may allow supercharger operation at higher speeds and loads than have been acceptable.

While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims. 

1. A positive displacement supercharger comprising: a housing including a rotor cavity having a surrounding cavity wall; a pair of positive displacement rotors oppositely rotatable in the rotor cavity and having interleaved helical lobes forming rotor chambers operative to carry air axially from an inlet end of the cavity to an outlet end of the cavity; a gear case received within the rotor cavity and drivably connected with and supporting the rotors at outlet ends thereof, the gear case including a bearing housing having an end surface facing the rotor cavity and the outlet ends of the rotors; and a heat insulating material applied to the end surface of the bearing housing and effective to reduce heat flow between the rotor cavity, with the rotors and compressed air therein, and the end surface of the bearing housing to effectively limit lubricating oil temperatures in the gear case.
 2. A supercharger as in claim 1 wherein the heat insulating material is a ceramic.
 3. A supercharger as in claim 2 wherein the ceramic is formed as a preformed plate.
 4. A supercharger as in claim 3 wherein the ceramic plate is secured to the end surface of the bearing housing by mechanical fasteners.
 5. A supercharger as in claim 3 wherein the ceramic plate is secured to the end surface of the bearing housing by an adhesive. 